Save File with Extension

Question

I would like to recover a file of the type blob, and to add the extension, without the user having to type this extension when recovering. The way it is, I’m saving and also recovering, but recovering without the extension.

I have the button attach, then the save button.

To recover the file (save in desired folder) I have the recover button.

Attach button:

private void jBAnexarArquivoActionPerformed(java.awt.event.ActionEvent evt) {                                                
    caminho = null;
    JFileChooser file = new JFileChooser();
    file.setFileSelectionMode(JFileChooser.FILES_ONLY);
    int i = file.showSaveDialog(null);
    if (i == 1) {
        JtextFieldLocalArquivo.setText("");
    } else {
        File arquivo = file.getSelectedFile();
        JtextFieldLocalArquivo.setText(arquivo.getPath());
        caminho = arquivo.getPath();
    }
}

Save button:

String path = caminho;
FileInputStream input = null;
File theFile = new File(path);
input = new FileInputStream(theFile);
byte[] bytes = IOUtils.toByteArray(input);
empresa.setAnexo(bytes);

Retrieve button:

private void jBRecuperarArquivoActionPerformed(java.awt.event.ActionEvent evt) {                                                   
    Connection con = new SQLConnection().getConnection();
    Statement myStmt = null;
    ResultSet myRs = null;
    InputStream input = null;
    FileOutputStream output = null;
    try {
        myStmt = con.createStatement();
        String sql = "select anexo from empresa where idEmpresa = '" + empresaIdField.getText() + "'";
        myRs = myStmt.executeQuery(sql);
        JFileChooser fileChooser = new JFileChooser();
        int returnValue = fileChooser.showOpenDialog(null);
        if (returnValue == JFileChooser.APPROVE_OPTION) {
            File selectedFile = fileChooser.getSelectedFile();
            String path = selectedFile.getAbsolutePath();

            output = new FileOutputStream(selectedFile);
            if (myRs.next()) {
                input = myRs.getBinaryStream("anexo");
                byte[] buffer = new byte[1024];
                while (input.read(buffer) > 0) {
                    output.write(buffer);
                }

            }
        }

    } catch (Exception exc) {
        exc.printStackTrace();
    } finally {
        if (input != null) {

            try {
                input.close();
            } catch (IOException ex) {
                Logger.getLogger(CondutorInfracaoView.class.getName()).log(Level.SEVERE, null, ex);
            }
        }
        if (output != null) {
            try {
                output.close();
            } catch (IOException ex) {
                Logger.getLogger(CondutorInfracaoView.class.getName()).log(Level.SEVERE, null, ex);
            }
        }
        try {
            con.close();
        } catch (SQLException ex) {
            Logger.getLogger(CondutorInfracaoView.class.getName()).log(Level.SEVERE, null, ex);
        }

    }
}                     

Answer 1

The simplest approach to use, since you have the original file, is to also save the file extension or the mime type.

Unlike how you’re doing, having a column of the kind blob on the table empresa, maybe a more organized way would be to have a relationship only for the attachments, something like that:

CREATE TABLE anexos (
    id int(11) not null,
    content blob not null,
    extension varchar(10) not null,
    empresa_id int(11) not null,
    constraint foreign key (empresa_id) references empresa (id)
)

As you can see, you would persist also the file type information, so you have simply the file extension, without worrying about trying to guess it after.

In case you don’t have the original file, only the binaries, there are some approaches to you recovering it, but there is no guarantee. Some of them are these (as you are creating a file, I am considering approaches starting from a File/Path):

• if using Java >= 7, use Files.probeContentType(path) to recover the mime type and then map to an extension, for example using the Apache Tika, something like that:

final File file = new File("F:/Java-8-Features.pdf");
final Path path = file.toPath();
final String mime = Files.probeContentType(path);

// apache tika
final MimeTypes types = MimeTypes.getDefaultMimeTypes();
final MimeType mimeType = types.forName(mime);
final String extension = mimeType.getExtension();
// faça o que for preciso com a extensão

• using Urlconnection.guessContentTypeFromStream(is)(almost never works) to recover the mime type and then map to an extension, for example using also the Apache Tika, but it would be something like this:

final InputStream is = rs.getBinaryStream("anexo");
final String mime = URLConnection.guessContentTypeFromStream(is);

// apache tika
final MimeTypes types = MimeTypes.getDefaultMimeTypes();
final MimeType mimeType = types.forName(mime);
final String extension = mimeType.getExtension();
// faça o que for preciso com a extensão

• make your own routine that checks the binary header. Each extension has its own header, so you could do something that misses these headers.

This Soen question has some interesting answers too: Determining Binary/text file type in Java?.